Finally, a Robot That Moves Kind of Like a Tongue

Your tongue is super weird, which is fine because mine is too. Even though it lacks supporting bones, it can move in all sorts of directions because it’s a “muscular hydrostat”: Fluid is compressed in different parts of the tongue, allowing it to wiggle all around. It’s the same idea behind the elephant’s trunk and the octopus’ famously dextrous arms.

And now that weird kind of muscle has inspired a bendy inflatable robot. Researchers at Harvard and Yale have developed a relatively simple kind of air-powered actuator—or the bit of the robot that produces motion—that can create a wide range of complex movements. And that could help push soft robots, which at the moment are severely limited in the ways they can move, into new territories. Think squishy machines with more of the dexterity that traditional robots enjoy, yet are far more compliant. Meaning, they won’t break you if you get in their way.

Let’s say you’ve got one of those long balloons for making balloon animals. If you blow air into it, it expands, getting longer and fatter. But if you were able to constrain the expansion along one edge, you could get it to curl. This new system does that with what are essentially fancy stickers embedded with unidirectional, inextensible fibers.

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Take a look at the GIF above. Two stickers with fibers running lengthwise constrain the balloon to make it turn as it inflates (such an actuator could also use hydraulics instead of air, by the way), while a third sticker with fibers running at a 45 degree angle make the balloon twist at the end. “By itself it's essentially a balloon, so if you would inflate it, it would just uniformly expand radially and elongate,” says Yale engineer Robert Baines, co-lead author on a new paper describing the system in Nature Communications. “But we've attached constraining stickers in such a fashion as to generate this compounded twisting, bending motion.”

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And here, you can see an engineer place a sticker with fibers running along the length of the balloon. When the balloon is inflated, the sticker keeps that side of the balloon from expanding like the opposite side does, which produces a curling motion.

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And notice in this GIF how at top left the material freely inflates, distorting the text. At top right, it’s constrained from expanding side to side, at bottom left it’s constrained up and down, and at bottom right it’s both.

So from a relatively simple mechanism, you can get an actuator that can twist all over the place. The beauty here is that the researchers have essentially built intelligence into materials, whereas to get a traditional actuator to move an arm in a particular way, you have to build intelligence into the control algorithms. And unlike a traditional robotic actuator, which uses a metal motor to move in static ways, this system comes with literal and metaphorical flexibility.

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“We can take this constraining sticker and adhere it to the surface of any expanding actuator to design the trajectory of motion so that expansion is directed in a certain way,” says Yale engineer Rebecca Kramer-Bottiglio, who led the work. “And then we can remove it and reapply it in a different location, or stack them at different angles or more complex patterns to create other trajectories.” That means the researchers can reuse balloons, modifying them to move in different ways on the fly.

Soft robots, though, still come with serious limitations. For one, these kinds of actuators have nowhere near the power of traditional motors, which allow robots on automotive assembly lines to heft massive pieces of metal. And materials in soft robotics are still a problem—if you spring a leak, you’re kaput, or you might outright pop. But materials are also a potential advantage of soft robotics: While traditional robot motors are stuck with metal, squishy robots could leverage newfangled materials that are both strong and compliant.

And soft robots are already coming to market. An aptly named company called Soft Robotics makes inflatable grippers for grasping delicate objects like eggs. And because an inflatable robot would bounce off you instead of tossing you across the room like a traditional robotic arm might, these kinds of machines might one day work alongside humans.

Matt Simon is a staff science writer at WIRED who is one of the few people on Earth to have witnessed the fabled mating ritual of the axolotl salamander. He does the weekly robotics video series HardWIRED and is the author of The Wasp That Brainwashed the Caterpillar, which won... Read more

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